Light valve



A. M. CUR-ns LIGHT VALVE Filed Nov. 26. 1930 2 Sheets-Sheet 1 /NvE/vToR 4. M. CURTIS ATTORNEY 9,1934. A, M. CURTIS 1,943,112

LIGHT VALVE nl ed Nov. 2s. 1930 2 sheets-sheet 2 /4 @f- /a 29 L, i l

INVENTOR By ,4.114. CURTIS 1 wif#- A TTORNEY Patented Jan. 9, 1934 PATENT OFFICE LIGHT VALVE v Austen M. Curtis, East Orange, N. J., assigner, by mesne assignments, to Western Electric Company, Incorporated, a corporation of New York Application November 26, 1930 Serial No. 498,257

This invention relates to indicating devices such as galvanometersand has special reference to improvements therein for increasing the efficiency of operation of such' devices.

This invention has particular reference to the type of galvanometer in which a conducting nbre or filament is maintained in a magnetic field and its movement observed or recorded when a current passes therethrough. Such instruments having a single fibre are employed for measuring small currents or as telegraphic or wireless receivers and those having a double string are employed with success in fllm sound much as C. above the surrounding air due to the heating effect of the current in the magnetic coil. This temperature variation will have a detrimental effect on the operation of the device in a manner to be described. The filament is usually attached to a holding or supporting member which is in turn attached to the body of the device. The supporting member and the body-ofthe device are usually made of iron while the filament itself consists cfa strip or wire of duralumin, aluminum, or some other suitable material. As the temperature coefllcient of expansion ofthe filament is greater than that of iron, expansion of the metals caused by the rise in temperature, is unequal. This results in an increase in length of the filament which is greater than the increase in distance between the supports, the effect being to reduce the tension in the lament. It is obvious that a reduction of the originallyv applied tension in the filament will decrease its natural period of vibration to a point which may be within the range of frequencies to be applied during operation.

Another cause of reduction in tension with change of temperature is produced by the change in elasticity of the material making up the lilaments. A rise in temperature will so change the elasticity of the material as to cause a resulting reduction of the originally applied tension.

The principal object of this invention is to pro-5 1,638,555, August 9, 1927, to E. C. Weiite.

vide an improved device oi the type described which will operate uniformly regardless of the effects of temperatures to which the device may be subjected in practice.

A feature ofthe invention lies in the provision of means associated with the fibre or filament to maintain constant the original tension applied thereto regardless of any conditions of temperature.

A further feature of the invention lies in the provision of a tension compensating member which is sensitive to slight temperature variations and which is adjustable so as to compensate for different degrees of temperature change.

Heretofore, the filament has been attached aty its end to a spring member which takes up any slack inthe lament caused by expansion of the lament with temperature. A disadvantage in this method of compensating for reduction in tension caused by expansion is that the spring member forms an important part of the vibrating system when low, frequencies are supplied to the filaments.

In accordance with this invention, means are provided in association with the tensioned nbre to automatically compensate for tension varia: tions therein produced by temperature changes. The filament or fibre is attached to a holding or supporting member made of so-called thermostat metal which consists of two metals having widely dissimilar coeicients of expansion welded together, so disposed with relation to the A dbre that a change in temperature will cause the support to act in such a manner. as to compensate for the resulting variation in tension of the fibre.

In order that the invention may be more clearly understood, reference is made to the accom-` panying drawings inl which:

Fig. lis a side elevation of alight valve section;

Fig. 2 is a plan view of the interior of the casing cover showing the general arrangement of the different adjusting 'and supporting devices;

Fig. 3 is an elevation partly in section of the 100 device shown in Fig. 2;

Fig. 4 is a detail oi.' the thermostatic supporting member for the movable element; and

Fig. 5 is a detail of an adjustable thermostatic supporting member for the movable element.

The accompanying drawings disclose the invention as applied to a light valve employed in film sound recording systems, the principle of operation of whichis disclosed in U../S. Patent of theV filament will likewise affect Referring to Fig. 1, the reference numeral 1 indicates a light valve casing provided with a cover 2 adapted to be held in definite position by projections 3 and secured to the casing by means of a knurled annular ring 4 which is provided with an internal screw thread to engage the thread 5 (Fig. 3) of the cover. The casing 1 contains a fleld winding 6 and one pole piece 7. A

strip 8 provides a mounting to which the field winding leads are attached to facilitate connection to an external source of current.

Referring now to Fig. 2 which shows a plan view of the interior of the casing cover, a pole piece 9 is secured to the casing cover by some suitable means such as screws. The pole pieces 7 and 9 have aligned apertures 10 and 11 respectively, through which light rays from a suitable light source are projected. A conductor or filament 12 forming the movable element of the valve is drawn across the pole piece 9, but is not in engagement therewith. The filament is then passed'around a pin 13 attached to an L-shaped member 14 of some suitable insulatng material. The lament isnext passed back over the pole piece 9 and terminated in a supporting member 15 which will be hereinafter discussed.` Ivory frets 16 are placed in the position shown to form a bearing surface or bridge for the filament.

In order to obtain accurate space relaton between the filaments 12 and keep them ment across the face of the pole pieces, two adjusting elements 17 and 18 are placed on opposite sides of the pole piece 9. 'Ihe adjusting device comprises a block of insulating material 17 shaped as shown and attached to the cover 2. This block 17 contains adjusting members 1ocated on opposite sides of the filament. 'Ihe adjusting members comprise pincer elements 19 and adjustment screws 20. The movement of the pincer members is accomplished by means of a vernier differential screw arrangement (not shown) actuated by the adjustment screws 20. Spacer studs 21 and 22 are affixed to the casing cover, and are of a height exceeding the coinbined height of the pole Vpieces an amount sufficient to allow the proper space between the pole faces. 'Ihe pin 13 around which the filament 12 is looped is attached to the L-shaped member 14 of suitable insulating material, which is flexibly connected by a .thin metallic strip 24 to an insulating block 25 secured to the casing cover by means of screws 26 and 27. Adjusting screws 28 and 29 are associated with the L-shaped member 14 and provide a means of applying the proper tension to the conductor or filament. By means of screw 28 proper tension may be applied and this applied tension maintained by means of a screw 29 in combination with a spring 30.

In" accordance with this invention the supporting members are constructed of so-called thermostat metal which consists of two metals having widely dissimilar coefficients of expansion welded together.

In Fig. 4 the supporting members 31 and 32 are shown as mounted in a block of insulating material 33 secured to the casing cover by means of screws 3'7 and 38. The ends of the filament are fastened to tapered pins 34 and 35 aflixed to the supporting members 31 and 32 respectively. These thermostat metal supports are arranged so that the metal having the higher coefcient of expansion is nearer the pole pieces. Therefore, an increase in the temperature of the surrounding air which might cause an expansion andlengthening the supports to cause them to bend-away from the pole pieces. As the ends of the filament are connected'to these supports, the decrease, in tension in these filaments'caused by their expansion will be compensated for by the simultaneous increase in the distance between the supports 31 and 32 andthe L-shaped member 14. It has been found that such fixed supports may be designed and employed to compensate for tension variations in filaments caused by all temperature changes encountered in actual operation. Sound modulating current is applied to the filament through conductors 42 and 43 which are connected to the binding posts 40 and 4l.

Fig. 5 discloses a detail of a V-shaped adjusts able supporting member. An upper arm 45 consists of a metal of higher coefiicient of expansion than the metal forming a lower arm 46. The filament 12 may be secured to the support by means of tapering pin 47. This type of support may be audjusted to compensate for 'different degrees of temperature change. 'I'he degree of compensation will be higher the closer the separate,arms 45 and 46 are placed to eachl other. Therefore, by changing the length of the base of the triangle of the height ofthe supporting member 48, the degree of compensation desired may beobtained. An increase in temperature affecting this support will cause the upper arm 45 to expand to a greater degree than the lower arm-46 thereby forcing the tapered pin 47 downward thus maintaining the tension in the filament 12 which has been expanded due to such temperature rise. j

While this invention has been described in connection with a light valve employed in sound recording, it is to be understood that it may be employed efiiciently in instruments of a similarv nature employing either one or more separate movable elements.

. It is obvious from the above description that with the use of thermostat metal supports as described the applied tension to the filament may be maintained for all operating temperatures.

What is claimed is:

1. In a light valve, the combination of means for producing a constant magnetic field, a pair of conductors supplied with modulated electrical currents suspended in said field, said conductors being tensioned to have a frequency of mechanical resonance above the highest frequency to be supplied with said modulated currents, and means for maintaining constant the frequency of mechanical resonance of said conductors at all operating temperatures, said means comprising similar bi-metal thermostatic supports for each of said conductors.

2. The combination in. a light valve having means for producing a constant magnetic field and a movable element suspended and tensioned in said magnetic field to have a frequency of mechanical resonance above any frequency likely to be supplied thereto during operation, of means for maintaining constant the frequency of mechanical resonance of saidelement at all operating temperatures, said means comprising a bimetal thermostatic support for said movable element. Y v,

3. The combination with an indicating device having a tensioned movable element suspended in a magnetic field of a bi-metallic support for said element, said support responsive to temperature changes in such manner as to maintain constant the Original tension in said movable element, AUISTEN M. CURTIS. 

